In recent years, a fuel cell stack has been mounted on automobiles or other vehicles due to its lowered influence on the environment. A fuel cell stack supplies, e.g., a fuel gas, such as hydrogen or the like, to the anode side of a fuel cell and an oxidizing gas containing oxygen, e.g., air, to the cathode side of the same, and obtains required electric power through electrochemical reaction occurring through an electrolyte membrane.
A cathode off-gas drained when the oxidizing gas supplied to the cathode side is drained from the fuel cell stack contains reaction-generated water generated in electrochemical reaction. Meanwhile, an anode off-gas drained when the fuel gas supplied to the anode side is drained from the fuel cell stack also contains reaction-generated water having passed through an electrolyte membrane of the fuel cell.
The anode off-gas is sent to a dilution device by opening, at a predetermined timing, a purge valve provided on a pipe connecting between the anode off-gas outlet of the fuel cell stack and the dilution device. The cathode off-gas as well is sent from the fuel cell to the dilution device through a pipe. In the dilution device, the anode off-gas is mixed with the cathode off-gas for dilution before being emitted to the outside. In the above, reaction-generated water contained in the cathode off-gas and the anode off-gas is also drained.
The pipe connecting between the anode off-gas outlet of the fuel cell stack and the purge valve and the pipe connecting between the purge valve and the dilution device are preferably disposed so as to descend toward downstream in the off-gas emission direction in order to reliably drain the reaction-generated water contained in the anode off-gas. Further, in order to ensure electrical insulation for the fuel cell stack between the purge valve and the dilution device, the purge valve and the dilution device are generally connected using, e.g., a rubber tube made of an insulating member. In this case, in order to ensure sufficient insulation for a high-voltage fuel cell stack, a rubber tube of some length must be used. When such tube is used, there must be ensured a height difference of e.g., a few tens of centimeters between the anode off-gas outlet of the fuel cell stack and the anode off-gas inlet of the dilution device in order to ensure drainability and sufficient insulation effect.
For example, Patent Document 1 discloses that a pipe for introducing water drained from a fuel cell system to an emission pipe is disposed descending toward downstream in a fluid flowing direction so that fluid can easily flow inside the pipe.    [Patent Document 1] Japanese Patent Laid-open Publication No. 2005-163812